Barclays plans to sell or exit most of its commodities businesses as part of an effort to shrink its investment bank and improve returns.

The UK bank will pull back from trading in base metals, energy and agricultural products and fold its precious-metals business into its currency-trading unit, people familiar with the plans said Monday. The move comes as Barclays prepares to tell investors on May 8 how it will reshape its investment bank—where the commodities business is housed—to adapt to costly new regulations and a slowdown in some business areas.

Martyn Whitehead, head of metals and mining sales at Barclays and the bank's representative on London's gold fixing panel, will leave the bank amid the changes, a person familiar with the matter said Whitehead declined to comment. His departure puts a question mark over whether Barclays will remain on the five-bank panel that sets the global benchmark price for gold each day.

Exiting commodities has been seen by analysts as a likely outcome of Barclays' review of its investment bank. Barclays and other banks have increasingly found it difficult to make acceptable returns in high-cost, low-margin global commodities trading, and the US Federal Reserve is considering putting fresh limits on banks' exposure to commodities markets to address concerns about potential conflicts of interest.

The UK bank shut down its US and European power-trading desks in February, after deciding they didn't meet "economic and strategic criteria." A spokesman said at the time that the decision wasn't related to a continuing, $436 million lawsuit by the US Federal Energy Regulatory Commission against the bank over alleged electricity price manipulation, a charge the bank is fighting.

Other parts of commodities markets also face regulatory action. The daily gold fix set by Barclays and four other banks is currently under review by international regulators as part of a wider probe into market benchmarks. The five banks are also facing several lawsuits by US investors who claim collusion over price manipulation.

Barclays Chief Executive Antony Jenkins has been looking for ways to sharpen Barclays' strategy since an initial push in February 2013 to set the bank's course was blunted by a slowdown in some of its core markets, particularly fixed-income trading. A drop in Barclays' share price this year reflects investors' concern that the company can't improve returns at its investment bank without a major shift in strategy, and has helped prompt Jenkins to become more aggressive in shrinking the unit.

On Thursday, he told staff in an internal memo that big changes in Barclays' shape and structure would be announced on May 8, and the company that day made a series of management changes in the investment bank to combine business areas and simplify the division.